CSE 341 - Programming Languages

Running Racket

We'll use DrRacket, version 6.2.1. It is installed on the windows and linux machines in the undergrad labs, or you can download it for a personal machine.

On the Windows machines in the lab, DrRacket is here:

All Programs / DEV TOOLS & LANGUAGES / Racket / DrRacket

You can also double-click on a saved Racket source file.

On Linux, start it by typing drracket to the shell prompt. You'll need to use XWindows -- DrRacket will come up in a separate window.

Finally, you can download it and install it on a personal machine from http://racket-lang.org/download. It's free.

First Time Set-Up

The first time you use DrRacket, click on “Language” in the top menu, then select “The Racket Language.” The text #lang racket should appear in the upper definitions pane, and the bottom left should say “Determine language from source“ Click “Run”.

DrRacket should remember this choice henceforth.

Structure of your Racket files

Create and save programs in the (top) “Definitions Window.” You can save your file wherever. Use a .rkt file extension.

Make sure that the first line of your file is exactly (including the # character):
```
     #lang racket
```
This tells DrRacket that your file is in the Racket language and not some other language. You can have lines of comments before this line.

For your homework, we recommend just using one file, including both the code and the unit tests. If you do want to use two files, one with the function definitions and another with tests, the cleanest way to make this work is to explicitly list in your definitions file all of the functions that you want to export. For example, if you have two fishy functions to export to the unit tester, use this:
```
     (provide tuna flounder)
```
Or as a hack, you can work around Racket's module system by making the second non-comment line of your file with function definitions be:
```
     (provide (all-defined-out))
```
In Racket, each file is its own module and this line is making all top-level definitions externally visible, which is not the default. You do not need this line to use your definitions in the REPL (the bottom buffer). You do need this line (or another approach) to use your definitions from a second testing file.

For a second testing file, also include the #lang racket line and then include the line
```
     (require "octopus.rkt")
```
where octopus.rkt is the file with the code you want to test. Put both files in the same directory/folder on your computer. Your testing file does not need (provide (all-defined-out)).

Using DrRacket

For the most part DrRacket is an easy-to-use system with lots of documentation. Here are a few specific notes related to how we will use it:

Click “Run” to have the REPL process the definitions in your file.

Clicking “Run” will “start the REPL over” -- all previous work will disappear and only the definitions from the file you “Run” will be defined.

If you want to save work in the REPL, do so before clicking “Run.” There is also an option under “File” for “Log Definitions and Interactions” but we have little experience with it.

The definitions pane has a snazzy GUI for showing the bindings of variables -- hover over a variable to see where it is bound, or what uses that definition.

A useful shortcut in the REPL on Windows is to use Alt-P (any number of times) to bring back up recent interactions. Moreover, this works even to bring up interactions from before the most recent “Run.” That is, even though the interactions disappeared and are not part of the current environment, you can still use Alt-P to bring them back and then edit them or click Return to re-run them. For Macintosh use Esc-P.

When using a second testing file as described in the previous section, click “Run” in the window that has the testing file. This will send to the REPL your homework solution and your tests.

If your program is stuck in an infinite loop, click “Stop.”

You can (re-)indent a line with the TAB key. You can select multiple lines and hit TAB to reindentall selected lines.

If you type ), DrRacket will replace it with ] if doing so will match a [.

Useful Tools

Use the "Debug" button to debug programs, and also to understand how recursive functions are operating. Another useful command is "Check Syntax", which of course checks the syntax, but also lets you see the bindings of variables. (Try hovering the mouse over a variable -- good to help understand lexical scoping.)

If you are working on a personal machine not connected to the Internet, installing Racket provides a local copy of the documentation -- the “help” menu item will access it.